Protective means for electrical devices



Feb. 22, 1955 A. E. MOOG 2,702,876

PROTECTIVE MEANS FOR ELECTRICAL DEVICES Filed Sept. 20, 1949 FIG. 1

l .J INVENTOR.

/ ARTHUR E. M006 F) rra /vf y United States Patent '0 PROTECTIVE MEANSFOR ELECTRICAL DEVICES Arthur E. Moog, Caldwell, N. J., assignor toBendix Aviation Corporation, Teterboro, N. J., a corporation of DelawareApplication September 20, 1949, Serial No. 116,794

2 Claims. (Cl. 317-45) The invention relates to electrical devices, andmore particularly to protective means therefor, and to the absorption oreummation of products of combustion when the devices overheat.

An overheated electrical device, such as a transformer, generates steam,ODIIOXIOUS rumes and smoke irritating to the nose and throat. if thehousing enclosing the device is sealed, the steam pressure may become sogreat as to rupture the housing, and permit the fumes and smoke toescape therefrom.

When such a device 18 used in aircraft, the pilot and passengers areseriously alarmed by the fumes and smoke which permeate the caom of thecraft. 'lhe pilot is often prompted to make an emergency landing withall its hazards rather than risk remaining airborne with the uncertaintyof a ma or failure, whereas only a minor piece or equipment may haveoverheated without meeting safe operation of the craft.

it is common practice to use a fuse in circuit with an electrical deviceto open the circuit during overheating, but the device cannot readily befused so that the circuit is opened before fumes and gas escape from thedevice.

One object of the present invention is to absorb prodnets of combustionwhen an electrical device overheats so that the fumes and smoke do notescape therefrom.

Another object is to provide an electrical device, having a sealedhousing and a fuse, with a substance to absorb moisture and otherproducts of combustion when the device overheats, so that steam pressurewithin the housing is maintained sufficiently low until the circuit isopened by the fuse and while the device cools, to prevent rupture of thecasing.

Another object is to embed the fuse in the windings of the coils orother wiring so that the fuse responds readily to overheating of thedevice.

The invention contemplates an odor absorbing substance associated withan electrical device subject to overheating to avoid odors when thedevice overheats. The substance preferably absorbs moisture also so thatwhen the housing of the device is sealed, pressure within the housingdue to steam is reduced to prevent rupture of the housing. The inventioncontemplates protecting the device by a fuse embedded in the wiring andhighly responsive to overheating of the device so that the steamgenerated during overheating is a minimum.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingwherein one embodiment of the invention is illustrated. It is to beexpressly understood, however, that the drawing is for illustration anddescription only, and is not to be construed as defining the limits ofthe invention.

In the drawing, Figure 1 is a front view of a transformer constructedaccording to the invention, with a portion of the front wall cut away tobetter show the construction.

Figure 2 is a schematic wiring diagram showing the circuit arrangementof the transformer.

Figures 3 and 4 are perspectives of the transformer windings showingdetails of construction.

In Figure 1, a three-phase transformer constructed according to theinvention has a hermetically sealed housing 1 adapted to withstandpressure of approximately pounds per square inch. The housing has afront wall 3, a rear wall 5, side walls 7, 9, a top wall 11, and abottom wall 13. A laminated core 15 is secured within housing 1 bybrackets 17. Core 15 has outer legs 19 and an inner leg 21. An outerphase winding 23 is wrapped on each outer leg 19, and an inner phasewinding 25 is wrapped on inner leg 21. The windings are connected byleads 27 to taps 29 on top wall 11.

Each outer phase winding 23 (see Figures 2 and 3) comprises an innerprimary coil 31 and an outer secondary coil 33 separated by suitableinterwinding insulation. A fuse 35 is positioned between the primary andsecondary coils in the insulation and is connected in series with theprimary coil.

Inner phase winding 25 includes successively wound secondary coils 37,39, 41, and a tapped primary coil 43. Suitable interwinding insulationis provided between each coil. A fuse 45 is positioned between secondarycoils 37, 39, in the associated interwinding insulation, and a fuse 47is positioned between secondary coil 41 and primary coil 43 in theassociated interwinding insulation. The fuses 45 and 47 are connected inseries with primary coil 43, as shown in Figure 2. With the arrangementdescribed, the fuses are intimately associated with the respective phasewindings, and a rise in temperature in the windings will be readilydetected by the fuses.

Before housing 1 is hermetically sealed, the entire air space within thehousing is filled with activated alumina 49, preferably of 8 to 14 mesh,which substantially surrounds core 15 and windings 23, 25.

When one or more of the windings in the transformer overheats, the fuseassociated with the overheated winding melts and opens the circuit inwhich the overheated winding is connected. Before the circuit opens, theinsulation and varnish on the overheated winding may give off productsof combustion, including moisture, smoke and obnoxious fumes comprisingdistillation products. The moisture, smoke and odors are absorbed by theactivated alumina, and any pressure that might otherwise be generatedwithin the housing, by moisture being converted to steam, is avoided sothat the housing ordinarily will not rupture. However, should thehousing rupture before the transformer cools, then the activated aluminaserves as a filter and absorbs the smoke and fumes so that the gasesemitted from the housing after rupture are without odor.

Other substances, such as barium oxide, having the absorbing qualitiesof activated alumina, may be used, but it is preferred to use asubstance which is nonconductive so that should excessive moisture beabsorbed by the substance, it will not short circuit the transformerwindings.

Although but one embodiment of the invention has been illustrated anddescribed in detail as embodied in a transformer, it is to be expresslyunderstood that the invention is not limited thereto and is applicableto motors, generators, amplifiers or to any other electrical equipmentsubject to overheating. Various changes can be made in the design andarrangement of the parts without departing from the spirit and scope ofthe invention as the same will now be understood by those skilled in theart.

What is claimed is:

1. An electrical device having a sealed housing, electrical componentsin said housing subject to overheating, a fuse in said housing connectedin circuit with said components to open the circuit when the deviceoverheats, there being activated alumina filling substantially theentire air space in said housing to absorb products of combustion and torelieve pressure in said housing to preillent rupture of the housingbefore said components coo 2. In a transformer, a sealed housing,primary and secondary windings in said housing, a fuse subject to thetemperature of said windings and connected in circuit with at least oneof said windings and adapted to open the circuit when said windingsoverheat, there being activated alumina in said housing to absorbproducts of combustion when said windings overheat to relieve pressureand prevent rupture of the housing before said components cool.

(References on following page) UNITED STATES PATENTS Hunter Nov. 6, 1894Ferrell Aug. 1, 1916 Greenwood Oct. 11, 1932 Hill Feb. 13, 1934 FordOct. 9, 1934 Brunner Dec. 15, 1936 Hill Oct. 10, 1939 Kater Mar. 26,1940 Nowak et a1. July 30, 1940 Anderson Oct. 10, 1944 Schaefer Feb. 20,1945 FOREIGN PATENTS Great Britain Aug. 15, 1929 Great Britain Dec. 9,1929 Great Britain Feb. 27, 1933? OTHER REFERENCES Related Materials,Gregory.

